1. Field of the Invention
The invention relates to a control circuit for a light-emitting diode and, more particularly, an arrangement which includes a switching or actuation stage or phase compensating for the impact of thermal conditions which affect the radiation effort or light output of a light-emitting diode.
2. Description of the Related Art
It is known that the emission or output .phi..sub.o of a light-emitting diode, hereinafter referred to as LED, at a given forward current or forward bias, I.sub.F, is a function of the temperature. NTC resistors or base-emitter portions of transistors have been employed to compensate for fluctuations of the output .phi..sub.o of LEDs caused by changes in temperature described, for example, in the technical journal "Elektronik", No. 26, 1984, page 90. Such circuits only compensate for relatively slow or "static" temperature fluctuations, and cannot compensate for momentary "dynamic" temperature fluctuations which are experienced during operation and which arise with temperature changes of the barrier layer of the diode due to the attendant power loss variations arising in the barrier layer.
A relatively linear relationship between the forward current I.sub.F and the output .phi..sub.o within the usual operating ranges of an LED is normally assumed in analog data transmissions in opto-electronic systems. Thus, changes of the radiation or output due to the fluctuation of the temperature of the barrier layer are normally not considered. In some applications such as high capacity analog opto-electronic data transmission systems, in which a direct intensity modulation or pulsed operation of the LED is effected, the non-linear behavior of LEDs cannot be disregarded as in digital opto-electronic data transmission systems.